📡 SAG Calculator
Calculate cable and wire sag for overhead installations
Distance between supports
Weight per linear foot
Cable tension at supports
How to Use This Calculator
Enter Span Length
Input the span length in feet - the distance between the two support points (poles, towers, etc.) where the cable or wire is suspended.
Specify Cable Weight
Enter the cable or wire weight in pounds per linear foot. This includes the weight of the conductor, insulation, and any ice or wind loading if applicable.
Set Tension
Enter the cable tension in pounds at the support points. This is the horizontal tension component. Higher tension reduces sag but increases stress on supports.
Calculate and Verify
Click "Calculate SAG" to see the sag, percent sag, and tension. Verify that sag provides adequate clearance above ground, obstacles, or other cables. Adjust tension if needed.
Formula
Sag = (Weight × Span²) ÷ (8 × Tension)
Percent Sag = (Sag ÷ Span) × 100
Where: Weight = lbs/ft, Span = feet, Tension = lbs
Example 1: Standard Cable (100 ft span, 0.5 lbs/ft, 500 lbs tension)
Step 1: Calculate sag: (0.5 × 100²) ÷ (8 × 500) = 5,000 ÷ 4,000 = 1.25 feet
Step 2: Calculate percent sag: (1.25 ÷ 100) × 100 = 1.25%
Step 3: Maximum sag occurs at the midpoint of the span
Example 2: Heavier Cable (150 ft span, 1.0 lbs/ft, 800 lbs tension)
Step 1: Calculate sag: (1.0 × 150²) ÷ (8 × 800) = 22,500 ÷ 6,400 = 3.516 feet
Step 2: Calculate percent sag: (3.516 ÷ 150) × 100 = 2.34%
Step 3: Verify clearance above ground or obstacles
About SAG Calculator
The SAG Calculator is an essential tool for electricians, engineers, utility workers, and anyone who needs to accurately determine the sag (vertical droop) of cables, wires, or conductors suspended between two support points. This calculator eliminates guesswork by providing precise sag calculations based on span length, cable weight, and tension, helping you ensure adequate clearance and proper installation.
When to Use This Calculator
- Power Line Installation: Calculate sag for overhead power lines and transmission cables
- Communication Cables: Determine sag for telephone and data cables
- Fence Wire: Calculate sag for fence wire installations
- Guy Wire Planning: Plan guy wire sag for tower and pole installations
- Clearance Verification: Verify adequate clearance above ground or obstacles
Why Use Our Calculator?
- ✅ Accurate Calculations: Precise sag calculations prevent clearance issues
- ✅ Percent Sag: Shows sag as percentage of span for easy comparison
- ✅ Clearance Planning: Helps ensure adequate clearance above ground or obstacles
- ✅ Time Savings: Instant calculations eliminate manual math
- ✅ Safety Planning: Ensures safe installation with proper clearance
- ✅ Easy to Use: Simple inputs for span, weight, and tension
Common Applications
Power Line Installation: Electricians and utility workers use this calculator to determine cable sag for overhead power lines. Accurate sag calculations ensure adequate clearance above ground, roads, and obstacles, and prevent cable damage.
Communication Cables: Technicians use this tool to calculate sag for telephone and data cables. Proper sag ensures cables don't touch ground or obstacles and maintain proper tension.
Fence Wire: Contractors use this calculator for fence wire installations. Proper sag prevents excessive tension that could damage posts while ensuring wires don't droop too low.
Tips for Best Results
- Measure Accurately: Use precise measurements for span length
- Cable Weight: Include weight of conductor, insulation, and ice/wind loading if applicable
- Tension: Use horizontal tension component at support points
- Clearance: Ensure sag doesn't cause clearance violations above ground or obstacles
- Temperature Effects: Sag increases with temperature - consider seasonal variations
- Ice Loading: Add ice weight in areas with freezing conditions
Frequently Asked Questions
What is cable sag?
Cable sag is the vertical distance a cable or wire droops at the midpoint between two support points. Sag occurs due to the weight of the cable and is maximum at the midpoint. Sag is important for clearance calculations and safety.
How do I calculate cable sag?
Sag = (Weight × Span²) ÷ (8 × Tension). For example, with 100 ft span, 0.5 lbs/ft weight, and 500 lbs tension: (0.5 × 100²) ÷ (8 × 500) = 5,000 ÷ 4,000 = 1.25 feet. The calculator does this automatically.
What affects cable sag?
Sag is affected by span length (longer spans = more sag), cable weight (heavier cables = more sag), and tension (higher tension = less sag). Temperature also affects sag - sag increases as temperature rises.
How much sag is acceptable?
Acceptable sag depends on clearance requirements. Power lines typically have sag of 1-3% of span length. Sag must provide adequate clearance above ground, roads, buildings, and other cables. Check local codes and regulations for specific requirements.
Does temperature affect sag?
Yes! Temperature significantly affects sag. As temperature increases, cable expands and sags more. As temperature decreases, cable contracts and sags less. Plan for worst-case conditions (maximum sag in summer, minimum clearance in winter).
Can I reduce sag by increasing tension?
Yes! Increasing tension reduces sag, but higher tension increases stress on supports and cables. There's a balance between sag and tension. Too much tension can damage cables or pull down supports. Use appropriate tension for your application.